This invention relates to sodium sulphur batteries comprising a plurality of separate cells within a container.
A sodium sulphur cell has a solid electrolyte, typically sodium beta alumina, which separates molten sodium from a cathodic reactant comprising liquid sulphur/polysulphides. In the event of the electrolyte material cracking, the sodium and sulphur will meet causing a vigorous chemical reaction. The hot polysulphide material and sodium together are extremely corrosive and will attack stainless steel. Failure of one cell in a sodium sulphur battery can lead to a leakage of this highly corrosive polysulphide material and this in turn can lead to the attack on the casing of other cells so propagating the failure throughout the entire battery.
Various safety precautions are taken to prevent or minimise any such risk. In particular, provision may be made for restricting the flow of the materials in each cell and coatings may be provided on the inner surface of the outer container of each cell to minimise or prevent any risk of corrosion of the material of the cell container.